1. Field of the Invention
This invention relates to superconducting alloys, and more particularly, to superconducting metal alloys in the beryllium-niobium-zirconium system comprising a glassy matrix in which superconducting species are supported.
2. Description of the Prior Art
In the past, various ductile superconducting wires made from Nb-Ti, Nb-Zr and Nb-Ti-Zr (with superconducting transition temperature T.sub.c about 10 K) and other ductile superconductors have been considered for constructing superconducting magnets, motors and generators. However, these ductile wires have had relatively low critical fields and low stability against high magnetic fields due to their poor thermal conductivity. To overcome this problem, these wires have been imbedded in a normal resistance matrix such as copper. However, such combinations have usually lacked sufficient physical strength to achieve high stability of performance in magnetic fields.
Novel glassy metal alloys in wire form have been disclosed by H. S. Chen and D. E. Polk in U.S. Pat. No. 3,856,513, issued Dec. 24, 1974. These glassy metal alloys are represented by the formula T.sub.i X.sub.j, where T is at least one transition metal, X is at least one element selected from the group consisting of aluminum, antimony, beryllium, boron, germanium, carbon, indium, phosphorus, silicon and tin, "i" ranges from about 70 to 87 atom percent and "j" ranges from about 13 to 30 atom percent. However, no superconducting compositions are disclosed therein.
Such glassy metal alloys, like oxide glasses rapidly quenched from the melt, lack any long range order and evidence X-ray diffraction patterns in which intensity varies slowly with diffraction angle. This is in contrast to crystalline materials, which possess long range order and evidence a rapidly changing intensity with diffraction angle.
Although a relatively high superconducting transition temperature T.sub.c of about 10 K has been observed in the prior art for disordered beryllium thin films, vapor-deposited amorphous or highly disordered films have not been demonstrated to be of practical use due to their thickness limitation (less than about 1000 A) and their thermal instability. Various attempts have been made to synthesize non-crystalline, or glassy, superconducting alloys because such alloys are generally ductile, which is not the case for many of the crystalline superconductors having high T.sub.c values. Some examples of these efforts include Pd.sub.35 Zr.sub.65 (T.sub.c =3.5 K) Au.sub.24 La.sub.76 (T.sub.c =3.3 K) and Rh.sub.20 Zr.sub.80 (T.sub.c =4.1 K).